### Calculating the nominal downward pressure of water tanks of known capacity is simple but do you know how the weight of the water tank is spread?

An example would be two versions of 10000 litre water tanks – one a standard vertical water tank, the other, a low profile version. Both these 10000 litre water tanks, when full, exert 10000 kilograms or 10 metric tonnes of downward pressure (assuming 1 litre of water weighs 1 kg). The standard 10000 litre tank is taller than the low profile tank so the standard version has a smaller surface area touching the ground (base) compared to the low profile version. The standard 10000 litre water tank is thus exerting 10 tonnes of downward pressure over a smaller surface area, i.e. more concentrated (think of a stiletto heal versus a flat boot heal, as an extreme analogy).

Why is it sometimes important to know how much pressure is being exerted per unit of surface area? Because this could affect how a base/floor or tank stand platform will be affected – important for builders, engineers and for checking whether existing structures will be able to support the weight. Body corporate of housing developments also sometimes specify what is allowed in terms of water tank support structures and minimum requirements.

#### Here are some calculations for the 10000l vertical tank vs the low profile tank:

**10000 liter standard vertical JoJo water tank**

Diameter = 2200 mm Radius = 1100mm = 1.1m (Height is 3080mm but not required for the calculation)

Area of base = Pi x (radius squared) = 3.14x (1.1 x 1.1) = 3.7994 metres squared

Weight of a full tank is 10000kg x Gravity = 10000kg x 9.81 metres/second squared = 98100 N

Downward Pressure = Weight/Area = 98100/3.7994 = 25819.866 Pa = **25.8 kPa per metre squared**

**10000 liter low profile JoJo water tank**

Diameter = 2520 mm Radius = 1260mm = 1.26m (Height is 2420mm but not required for the calculation)

Area of base = Pi x (radius squared) = 3.14x (1.26 x 1.26) = 4.9851 metres squared

Weight of a full tank is 10000kg x Gravity = 10000kg x 9.81 metres/second squared = 98100 N

Downward Pressure = Weight/Area = 98100/4.9851 = 19678.642 Pa = **19.7 kPa per metre squared**

**Results:**

The 10000l JoJo vertical water tank exerts a downward pressure of 25.8 kPa per metre squared and the 10000l JoJo low profile water tank exerts 19.7 kPa…quite a substantial difference!

In normal situations, a well-built concrete base using 25 mPa cement appropriately thick will support either 10000 liter tank with ease. However, where it may not be possible to build a proper base, the 10000l low profile tank would spread its 10 tonnes of weight over a bigger surface area.

The above calculations are taken into effect when engineers design and construct steel water tank stands. This is why we always recommend JoJo steel water tank stands as they are designed and manufactured by a professional structural engineer with more than 37 years of experience. Do not trust steel tank stands that have been arbitrarily put together by a backyard handyman as if one of these fail, tonnes of falling water tank will destroy nearby structures and could harm anyone unfortunate enough to be around.

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